In recent years, human activities and industrial civilizations have brought enormous material wealth to the society, but they have also led to excessive consumption of natural resources and energy. The melting of glaciers and thus the rise in ocean levels as a result of global warming have become a global issue. Countries worldwide have united actively and are engaging in seeking solutions to lessen the tendency of the global warming. The Conference of Parties to the United Nations Framework Convention on Climate Change concluded successfully on 12 Dec. 2015 in Paris, France. 195 Parties adopted the Paris Agreement, which is a historic new agreement on climate change. A Large emission amount of carbon dioxide is the greatest root cause of the global warming, and combustion of coal to generate power is a major source of carbon dioxide emission. Currently, most coal-fired power plants discharge carbon dioxide directly into the atmosphere without any treatment. Only a small number of power plants perform capture and separation for the discharged carbon dioxide, which is then transported through pipes to a subsurface formation suitable for carbon dioxide sequestration, such as a depleted oil field, a deep saline aquifer or an unworkable seam, for long term sequestration or for oil and natural gas production. However, these methods are actually limited by geographic areas. There is no formation suitable for carbon dioxide sequestration or natural hydrocarbon reservoir near many power plants. In this case, if the discharged carbon dioxide is transported long distances by pipelines to a site suitable for sequestration or oil and natural gas production, investment costs would be substantially increased, and there would be a risk of leakage of the carbon dioxide from the pipelines.
The coal-fired power plants may produce lots of solid waste such as slag and ash. Taking Huaibei power plant as an example, its load is 4*200 MW, an annual volume of ash production is 730 thousand tons, and an annual volume of slag production 81 thousand tons. Currently, the slag and the ash are directly discharged as solid waste by most of the power plants. Discharge and storage of the solid waste may cause a serious environmental problem and a pressure on the society. Firstly, a lot of land may be taken by stacking a number of the discharged slag and ash. For this, cultivated area of local residents may be substantially decreased, and stacks of the discharged slag and ash may generate a great amount of dust which can seriously contaminate the air environment and affect normal life of the local residents. Further, under the action of rain, the slag and the ash stacked may flow into local rivers and lakes, and infiltrate into underground. This may cause contamination of local irrigation water and drinking water, thereby seriously affecting the health of the local residents. A lot of coal gangue which can not be recycled is produced during the process of coal mining for some pithead power plants, and the land and water resources may also be seriously contaminated by stacking a number of the coal gangue.
After coal mining is finished, the underground coal mine becomes a depleted one. Due to removal of a lot of coal, the depleted coal mine becomes a huge cavity. Support for the ground is thus absent, and problems such as cracking or collapse of the ground, landslide, debris-flow, and water and soil loss could be caused under a long time of seepage of rainwater. The surrounding air and hydrologic environment could also be seriously destroyed accordingly, and life safety and property safety of the local residents could be under serious threat.